feat(nix): add Nix flake for reproducible builds and demos

[randomizedcoder]

G'day Chris,

Thanks for your great YouTube videos and this project. This kinda blew my mind, and so I wanted to try it out on NixOS. Not sure if you've used Nix, but you might be interested if you haven't. I don't expect you to actually maintain the Nix, but it will make it easy to use for people using Nix. Please see the ./nix/README.md for full details.

What this adds

A modular Nix flake (flake.nix + nix/ directory) that provides:

• nix develop — reproducible dev shell with Rust toolchain, OpenBLAS, protobuf, Python/maturin, debuggers, and all build dependencies pre-configured
• nix build — builds the larql CLI binary (workspace minus larql-python)
• Pre-fetched model catalog — 8 models (Qwen, Phi, TinyLlama, StableLM, Gemma 4) as fixed-output derivations cached in /nix/store
• nix run .#demo — one-command walk of the default model (gemma4-4b)
• nix run .#repl / nix run .#repl-<key> — interactive REPL with a model auto-loaded
• nix run .#container — OCI container image via dockerTools
• Cross-platform — Linux (OpenBLAS) and macOS (Accelerate + Metal) support

Remote usage (no clone needed)

# From this fork (nix branch)
nix run github:randomizedcoder/larql/nix#demo

# Once merged to main
nix run github:chrishayuk/larql#demo
nix develop github:chrishayuk/larql

Files added/changed

File	Purpose
flake.nix	Small orchestrator (~73 lines)
flake.lock	Pins nixpkgs + flake-utils
nix/package.nix	Rust package derivation
nix/shell.nix	Dev shell config
nix/models.nix	8-model catalog with pre-computed hashes
nix/demo.nix	Demo/REPL run targets
nix/container.nix	OCI container image
nix/banner.nix	Dev shell welcome (uses your LARQL ASCII art)
nix/patches/use-system-protoc.patch	Uses nixpkgs protoc instead of bundled protobuf-src
nix/README.md	Full documentation
nix/example-queries.md	Example LQL queries
.gitignore	Un-ignores Cargo.lock, adds result
Cargo.lock	Now committed (required by Nix, recommended for binaries)

Non-invasive

• Zero changes to Rust source code — all platform fixes are applied via cargoPatches at Nix build time only
• The patch removes protobuf-src (uses system protoc), disables the metal default feature (re-enabled on Darwin via build flags), and adds #[cfg(feature = "metal")] guards — none of this touches your repo's actual source files
• Cargo.lock is now committed per Cargo's recommendation for applications/binaries

Test plan

• nix flake check passes
• nix build produces working ./result/bin/larql
• nix develop drops into dev shell with correct tools
• nix run .#demo walks gemma4-4b model
• nix run .#repl opens interactive REPL with model loaded
• Tested on NixOS Linux (x86_64)

Cheers! 🍻

🤖 Generated with Claude Code